5

4325.1

November 3, 2005

Functional Description

Initialization

The HIP6013 automatically initializes upon receipt of power.

Special sequencing of the input supplies is not necessary.

The Power-On Reset (POR) function continually monitors

the input supply voltages and the enable (EN) pin. The POR

monitors the bias voltage at the VCC pin and the input

protection). With the EN pin held to VCC, the POR function

initiates soft start operation after both input supply voltages

exceed their POR thresholds. For operation with a single

before POR initiates operation.

The Power-On Reset (POR) function inhibits operation with

the chip disabled (EN pin low). With both input supplies

above their POR thresholds, transitioning the EN pin high

initiates a soft start interval.

Soft Start

The POR function initiates the soft start sequence. An

internal 10

µA current source charges an external capacitor

amplifier output (COMP pin) and reference input (+ terminal

of error amp) to the SS pin voltage. Figure 3 shows the soft

amplifier (COMP pin) controls the converter’s output voltage.

At t1 in Figure 3, the SS voltage reaches the valley of the

oscillator’s triangle wave. The oscillator’s triangular

waveform is compared to the ramping error amplifier voltage.

This generates PHASE pulses of increasing width that

charge the output capacitor(s). This interval of increasing

pulse width continues to t2. With sufficient output voltage,

the clamp on the reference input controls the output voltage.

This is the interval between t2 and t3 in Figure 3. At t3 the

SS voltage exceeds the reference voltage and the output

voltage is in regulation. This method provides a rapid and

controlled output voltage rise.

Over-Current Protection

The over-current function protects the converter from a

shorted output by using the upper MOSFET’s on-resistance,

converter’s efficiency and reduces cost by eliminating a

current sensing resistor.

The over-current function cycles the soft-start function in a

programs the over-current trip level. An internal 200

µA

a 10

µA current sink and inhibits PWM operation. The soft-

with the error amplifier clamped to the SS voltage. Should an

complete its cycle. Figure 4 shows this operation with an

overload condition. Note that the inductor current increases

over-current trip. The converter dissipates very little power

with this method. The measured input power for the

conditions of Figure 4 is 2.5W.

TIME (5ms/DIV)

SOFT-START

(1V/DIV)

0V

0V

t1

t2

t3

OUTPUT

(1V/DIV)

VOLTAGE

FIGURE 3. SOFT-START INTERVAL

HIP6013